1. 下列方程组是三元一次方程组的是 ()
A.$\left\{\begin{array}{l} x+y= 1,\\ y+z= 2,\\ z-x= 3\end{array} \right. $
B.$\left\{\begin{array}{l} x+y+z= 0,\\ x-2yz= 3,\\ y-z= 10\end{array} \right. $
C.$\left\{\begin{array}{l} x^{2}+2y= 1,\\ y+z= 5,\\ x-z= 4\end{array} \right. $
D.$\left\{\begin{array}{l} x+y= 5,\\ w+z= 6,\\ z+x= 3\end{array} \right. $

A

)
A.$-2$
B.$2$
C.$-3$
D.$3$

D

3. 三元一次方程组$\left\{\begin{array}{l} x+y= 3,\\ y+z= 5,\\ x+z= 4\end{array} \right. $的解为 ()
A.$\left\{\begin{array}{l} x= 1,\\ y= 3,\\ z= 2\end{array} \right. $
B.$\left\{\begin{array}{l} x= 2,\\ y= 1,\\ z= 3\end{array} \right. $
C.$\left\{\begin{array}{l} x= 3,\\ y= 2,\\ z= 1\end{array} \right. $
D.$\left\{\begin{array}{l} x= 1,\\ y= 2,\\ z= 3\end{array} \right. $

D

4. 解方程组$\left\{\begin{array}{l} 2x+3y= 8,\\ 3x-2y= -1\end{array} \right. $的思路可用下面的框图表示,圈中应填写的对方程①②所做的变形为 ()

A.$①×2+②×3$
B.$①×2-②×3$
C.$①×3-②×2$
D.$①×3+②×2$

C